l»t, 1 Agriculture
Research Direction generate
Branch de la recherche
Technical Bulletin 1 988-4E
CCDE 88/03/10 NO.
LIERARY/BIBLIOTHEQUE OTTAWA KlA OC5
630 . 72
A.M. HARPER and D.W.A. ROBERTS
Research Station, Agriculture Canada
Technical Bulletin 1988-4E
Lethbridge Research Station Contribution No. 13
Copies of this publication are available from
Dr. K.W. May
Chairman, Phytotron Committee
Cereal Crop Science Section
Research Branch, Agriculture Canada
Published by Research Program Service
© Minister of Supply and Services Canada 1988
Cat. No.: A54-8/1988-4E
The dots on the map represent Agriculture
Canada research establishments.
SUMMARY/ RESUME ii
Plant growth cabinets 2
Plant growth rooms 3
Controlled temperature rooms with limited light 4
Headerhouse facilities 5
PLANS OF PHYTOTRON AREA 6
BASIC CONSIDERATIONS FOR CONTROLLED ENVIRONMENTS 7
Benefits of controlled environments 7
Refrigeration systems 8
Temperature measurement 11
ENVIRONMENTAL CONDITIONS 16
Cold rooms 16
Plant growth cabinets and rooms 16
Air movement 23
Nutrition and media 27
Carbon dioxide 28
Other gases 29
Diseases and pests 29
MANAGEMENT OF FACILITIES 33
GUIDELINES FOR REPORTING PHYTOTRON EXPERIMENTS 34
Light 3 5
Relative humidity 35
Carbon dioxide 35
Air movement 36
Containers, media, and nutrients 36
REFERENCES AND SUPPLEMENTARY READING 37
1. Summary of responsibilities 41
2. Plant growth rooms 42
3. Plant growth room benches 43
4. Experimental rooms with limited light 44
5. Phytotron program form 45
6. Phytotron work order form 46
7. Shut down and program change reguest form 47
8. Preventative maintenance form 48
9. Climatic data for Lethbridge 49
A. Air temperature
B. Frost data
C. Soil temperature
D. Degree days
F. Probability of growing season rainfall
10. Standard abbreviations 52
11. Conversion factors 53
12. Cornell mix 54
13. Hoagland's solution 54
14. Conversion of light units 55
This publication was written primarily to provide information about the
Lethbridge Research Station Phytotron for new staff members. The
publication also provides an overview of some of the problems with
controlling environmental factors in the Phytotron. These problems need
to be considered by all scientists when interpreting the results of their
Many scientists, engineers, architects, and administrators interested in
planning new Phytotrons have visited the Lethbridge Research Station
Phytotron and many have requested the type of information presented in
The authors were on the planning committee for the Lethbridge Research
Station Phytotron and have been involved with it since the start of its
operation in 1976. Dr. A. M. Harper, an entomologist, was Chairman of
the Phytotron Committee and managed the Phytotron and the preceding
greenhouse and growth chamber operations from 1970-1986. Dr. D. W. A.
Roberts, a plant physiologist, was Chairman of the Controlled Temperature
Rooms Committee and a member of the Phytotron Committee from 1970-1987,
and was instrumental in having the first plant growth cabinets constructed
at the Research Station in the 1950 's.
Several books have been written on Phytotrons and their authors have
discussed in detail the problems they have encountered. Consequently,
the effects of radiant energy on the aerial parts of plants have been
well documented. We have only briefly summarized this subject area.
Since one of the interests at Lethbridge has been the area of cold
hardiness and growth at low temperatures, especially of cereals, and
since the problems that have been encountered in this area have not been
adequately covered by other authors, these subjects are covered in detail
in this publication. Our experiences should be valuable to researchers
working under conditions where similar but much less pronounced problems
are to be expected.
- 11 -
Plans and physical features of the Phytotron at the Agriculture Canada
Research Station, Lethbridge, Alberta, are presented, with information on
its operation and management. The advantages and uses of the Phytotron
and its limitations are discussed, particularly the accurate control of
environmental factors. Guidelines for reporting Phytotron experiments
are given and references and supplementary reading are listed.
Le manuel contient les plans et les caracteristiques du phytotron de la
station federale de recherches agricoles de Lethbridge de meme que des
renseignements concernant son fonctionnement et sa gestion. On y discute
de ses avantages et de ses utilisations et, en particulier, du controle
precis des facteurs ambiants. On y trouve enfin des lignes directrices
sur la fagon de preparer les rapports sur les experiences avec le phytotron
ainsi que des references et une liste de lectures supplement aires.
The Phytotron is a system of controlled environment facilities designed
and operated for investigating relationships between plants and their
environment. In the Phytotron several physical parameters of the
environment including light quality and intensity, day length, air
temperature, humidity, plant nutrition, and concentration of gases can be
Because the Phytotron accelerates many phases of agricultural research,
results can be obtained several times faster than in the field or
greenhouse. A Phytotron can be used to obtain accurate knowledge of
plant reactions to environmental factors. This information is difficult
to obtain in the field where these factors are variable and almost
Phytotrons have been useful for studying and developing new varieties of
crops that have a short growing season, are winter hardy, drought
tolerant, or disease or insect resistant. They have also been valuable
for studying plant physiology; insect and disease biology, development,
and control; denitrif ication by soil organisms; plant nutrition; movement
of nutrients, salts, and water in the soil; and the biology, growth, and
control of terrestrial and aquatic weeds.
The Phytotron at Lethbridge Research Station was opened in 1976 and was
an expansion of eight greenhouses and 16 growth cabinets that were
constructed locally or were purchased between 1957 and 1970. The present
Phytotron consists of 67 growth cabinets, 23 growth rooms, and 10
In addition, there is a series of 22 controlled temperature rooms with
limited light that are used in conjunction with the Phytotron. The
Research Station also has extensive controlled environment facilities for
rearing and studying insects, and for studying animal parasites on both
small and large animals.
The Phytotron is available to scientists at the Research Station,
visiting scientists, Post-doctorate Fellows, and graduate students
working with Research Station scientists.
- 2 -
Plant growth cabinets
There are 67 plant growth cabinets in the Phytotron of which 11 are
0.65 m 2 in growth area, 6 are 1.40 m 2 , 2 are 1.67 m 2 , and 48 are
3.35 m 2 . All the 0.65 m 2 cabinets are a reach-in type with only one
door. The 1.4 m 2 cabinets are a reach-in type with two doors on one
side, the 1.67 m 2 cabinets are reach-in types with one door on each
side of the cabinet, and 45 of the 3.35 m 2 cabinets are reach-in types
with two doors on each side. Three of the 3.35 m 2 cabinets are a
walk-in type with a vestibule on one side which gives access to the plant
growth area from only the one side.
Two of the 3.35 m 2 cabinets have high ceilings (2.4 m) for growing tall
crops such as corn. Five of the 3.35 m 2 cabinets have humidity
control. One of these cabinets has humidif ication by steam and spray
nozzles, and four have humidif ication by spray only. Four of the five
cabinets have refrigeration-reheat dehumidif ication and the other cabinet
can be fitted with a chemical dehumidif er. Two of the 1.40 m 2 cabinets
are gas-tight, with gas ports, for studies with carbon dioxide or other
gases. Each of the 0.65 m 2 growth cabinets and nine of the older 3.35 m 2
cabinets have air-cooled condensing units and are completely independent.
The other cabinets are independent except for cooling water for the
water-cooled condensing units. Each growth cabinet has a shut-off valve
for the cooling water so that the unit can be repaired without affecting
other units. The cooling water system is in segments so that only one or
a few units need to be closed down to repair a breakdown in one of the
lateral lines. If the entire system fails, units can be kept operating
by connecting them directly to the domestic water supply.
The cabinets maintain accurate air temperatures (+ 0.5°C) in the range of
-10 to 40°C, 5 to 40°C, or 10 to 40°C. The 13 cabinets that operate from
-10 to 40°C have dual evaporators. Each cabinet has or will soon have an
electronic programmer for setting and maintaining all programs. The
cabinets can be programmed and monitored at the cabinet or at a central
One special area of the Phytotron is the Disease-Vector Laboratory where
there are three rooms. One room contains seven 0.65 m 2 cabinets, one
room contains four 0.65 m 2 cabinets, and the third room is an examination
and transfer room. The cabinets are used for maintaining cultures and
conducting experiments with insects and mites that transmit plant
diseases. The plants in the cabinets are watered by a glove-sleeve
insert in the locked door, and only the scientist and the technician
working with the disease and insects or mites have access to the
cabinet. When the plants are to be changed the cabinet is disconnected
and moved to the examination room where the vectors are transferred to
new plants. The old plants and all the debris are placed in plastic bags
in the room and are discarded. The room is then thoroughly cleaned and
the bench top washed with alcohol. During more than 10 years of
operation no areas of the Phytotron have become infested from the
- 3 -
Plant growth rooms
There are 23 plant growth rooms with 45 plant growth beds that vary in
size from 5.5 to 7.3 m 2 . The total room area is 602 m 2 of which the
total plant growth area is 315 m 2 . The plant growth area constitutes
51% of the total room area, and the aisles, which give ready access to
the plant growth area, take up the other 49% of the room area. All
refrigeration, heating, programming, and other equipment are in service
corridors that are adjacent to but completely removed from the plant
growth rooms .
The service corridors contain nearly all the services that are needed in
the rooms or by the machinery, such as electricity, compressed air,
distilled water, demineralized water, and water from the community water
supply. In our building the service corridor is the return duct for the
building air conditioning. For this reason, the natural gas pipes are in
the plant growth rooms as it is illegal to have them in the service
corridor. The service corridor is also large enough to permit ready
access to all machinery and removal of any part of the equipment used to
condition the environment in the plant growth rooms.
Each room is completely independent except for cooling water. All rooms
are now controlled by electronic programmers or will soon be fitted with
Most of the growth beds are approximately 1.4 m wide by 5.0 m long and
many have access from both sides. The facilities were designed so that
researchers would not have to reach more than 0.7 m to pick up or examine
a pot or plant.
Nineteen of the plant growth rooms are 2.4 m high. Four rooms, each with
two plant growth areas, are 3 m high to permit normal growth of tall
crops such as corn, and for the study of soils where plants are grown to
maturity in large containers with a soil depth of 1 to 1.5 m. One room
has a specially reinforced floor to withstand the weight of large amounts
Tanks for controlling soil and air temperatures separately are available
in four growth rooms. The soil temperature is controlled in narrow tanks
by temperature-controlled water in which the pots are almost fully
immersed. Air around the plants is controlled by the vertical movement
of air from growth benches beneath the tanks. The plumbing for the soil
temperature control can be readily removed and the beds can be used as
normal plant growth beds.
There are 10 greenhouses with 45 compartments and a total area of 1950 m 2
Greenhouses are single-glazed, and each compartment has supplementary
heating, lighting, and cooling with evaporative coolers. One greenhouse
compartment has an electronic controller that controls the temperature
more accurately than in the greenhouses with thermostats only. It opens
- 4 -
and closes the vents and controls the supplementary heating, cooling, and
lighting. During the summer some of the greenhouses are shaded with
metal blinds, and some with whitewash. None of the greenhouses is cooled
by mechanical refrigeration because of the cost. The heating system is
adequate to maintain the required temperature for plants when the outside
temperature is at -40°C.
Benches in all greenhouses are metal and all floors are concrete. When
high humidity is needed in a greenhouse, water is sprayed on the floor
several times a day, or electrical humidifiers are placed in the
compartment. Metal benches and concrete floors are used for cleanliness
and to make the control of insects, mites, and diseases easier.
Controlled temperature rooms with limited light
Associated with the Phytotron are 23 rooms with controlled temperatures
and limited light. (See Appendix 4 for room temperatures and dimensions.)
Twelve of these rooms are maintained at constant predetermined
temperatures and divided equally into two groups. One group usually
contains rooms at 25, 20, 15, 10, 5°C, and a spare. The spare room is
used at various temperatures usually near the freezing point with the
proviso that if one of the other rooms breaks down the scientist using
the spare room must vacate it immediately. The spare room is then set at
the temperature of the room that failed and maintained there permanently
or at least until repairs are made. Often the room that failed becomes
the new spare room. Rooms in the other group are run at 0.7 to 0.8, -5,
-10, -15, -20°C, and a programmable low temperature. One room is run at
0.7 to 0.8°C instead of 0°C to avoid freezing of exposed moist soil or
vermiculite as explained later in the section on cold rooms. These rooms
require frequent defrosting and are operated with defrosts every 4
hours. The programmable low temperature room is used for studies on low
temperature pathogens (snow molds). It has a programmer that permits
gradual controlled lowering of air temperature and its evaporator is
designed to reduce the frequency of defrosting.
One cold room provides extra cold storage at -20°C and two others provide
storage at -40°C. A third room at -40°C is reserved for storage of
pesticide-laden material from the field that is awaiting chemical
Two rooms are designed and operated for vegetable storage at temperatures
just above freezing. These rooms have additive humidity control (steam
generators). With the changing research program these rooms are now
operated at 1 and -10°C (+ 0.5°C) and are used in a program to select
cold-resistant lines of winter wheat. This change illustrates the
possibilities of adapting a controlled temperature room facility to
changing research requirements.
- 5 -
Three other rooms are operated just above the freezing point (4 to 5°C)
for storage of insect-damaged plant material and diseased plants. One of
these rooms is used for diseased potato storage and has additive humidity
control (steam generator).
One programmed cold room is used to freeze plants in connection with
studies on hardiness. It has an evaporator which is designed to provide
long periods (4-5 days) between defrosts at sub-zero temperatures rather
than the 4 hours between defrosts in the 12 temperature rooms described
above. The cold room with the long period between defrosts does not
provide temperature control as accurate as in rooms with the short time
Finally, there is a seed storage room which is run at 5°C. This room has
a dryer that keeps the relative humidity below 20%. It is used only for
long-term storage of genetic stocks. All seed material is inspected for
pests before it is placed in the room and yearly thereafter. Infested
material found in the room is removed and treated to destroy the pests
before it is returned to the room.
The following rooms and areas are in a headerhouse adjoining the main
portion of our Phytotron and are used in conjunction with it:
Vegetable research laboratory
Plant physiology laboratory
Insect and disease assessment laboratory
Plant dissection, examination, and washing laboratory
Eguipment and plant washing room
Seed storage room (temperature and humidity controlled)
Pesticide-laden plant storage room (-40°C)
Garbage storage room (air-conditioned)
Plant drying room (small and large dryers)
Plant nutrient preparation room
Pot and material storage rooms
Plant spray room
Fungicide, insecticide, and fumigant storage room
Soil and plant grinding room (with special dust removers)
Soil storage and mixing rooms
Storage room for special soils in containers
Equipment maintenance room
Potting, seeding, and examination benches
Service trucks can be driven into the main area of the headerhouse to
load and unload materials. Soil is loaded into the soil bins through
doors to the exterior that open into each bin.
- 6 -
PLANS OF PHYTOTRON AREA
A= standard cabinet (5 to 40 °C)
B= growth bench (5 to 40°C)
C= temperature room,
limited light (-40 to 40°C)
F = air-cooled small cabinets in
disease-vector room (5 to 40°C)
LT= low temperature cabinet (-10 to 40°C)
RR= controlled humidity cabinet
(refrigeration reheat) (5 to 40 C)
HC = high ceiling cabinet (5 to 40°C)
V « vestibule (5 to 40"C)
VLT = vestibule, low temperature
(-10 to 40°C)
B = growth bench
(5 to 40°C)
- 7 -
BASIC CONSIDERATIONS FOR CONTROLLED ENVIRONMENTS
Benefits of controlled environments
The introduction long ago of the greenhouse started freeing the plant
scientist from the vagaries of the field. In the last 50 years in Canada
the development of completely artificial environments for growing plants
has provided a quantum leap forward in this direction.
The first, but probably not the most important, advantage of the Phytotron
is its capacity for the production of crops on a year-round basis in
northern climates. Furthermore, uniform materials for biochemical,
physiological, entomological, pathological, and genetic studies can be
produced so that experiments can be planned and spread over the entire
year, as desired, to utilize staff efficiently. This stands in strong
contrast to the greenhouse where wintertime production of plant material
is often limited by short day lengths and low light intensities.
Greenhouse production in summer requires supplementary cooling.
In a Phytotron it is possible to adjust conditions so that hybridization
can be done at any time during the year and good seed set can be obtained
for early generations of a breeding program. This shortens the duration
of breeding programs by several years. Consequently, a new generation may
be started very soon after the parent plants set seed. In this way three
generations per year of cereals and six generations of faba beans can be
Controlled environments are advantageous for pathological studies since
environmental conditions often control infestation and may alter
resistance, such as with cereal bunt or disease expression in ring rot of
potatoes. With controlled environment facilities it is possible to
identify the environmental factors influencing the changes in resistance
or disease expression.
The greatest advantage to be gained from the use of the Phytotron is the
control of growing conditions. Controlled environment facilities have,
for example, made possible a much more accurate picture of the conditions
that affect cold hardening of wheat in the field. The use of such
facilities has made it clear that there is more to temperature effects
than just increased hardiness with lowered temperature within specified
limits. These facilities have made possible an explanation of why
killing occurs in late winter and early spring and have permitted the
development of a technique for testing hardiness which can be used to
select for resistance to such killing.
Detailed work on the genetics of cold hardiness in wheat is an example of
a study that would be almost impossible without controlled environment
facilities for hardening and hardiness testing. In the field,
winterkilling is variable from one part of a field to another and is
often all or none. Many tests are lost because of a lack of differential
kill. Winters are sufficiently variable and unpredictable that it is
impossible to select a site that will give consistent winterkilling due
to low temperatures. Furthermore, in the field winterkilling may be
- 8 -
caused by disease. Differential kills on tender material for genetic
studies require short mild winters, whereas long cold winters are
required for differential kills on very hardy materials. Such places in
the field are usually widely separated, often by hundreds of miles.
In order to gain maximum advantages from the use of a Phytotron, its
operation and limitations must be understood. This understanding is
essential for the proper interpretation of experimental results. For
this reason these limitations are discussed in detail in the section on
environmental conditions. It is the authors' hope that this discussion
will lead to the design of special equipment to overcome some of the
limitations and so make possible a better understanding of the effect of
the environment on plant growth and crop production. Such an understanding
should eventually assist the plant breeders in developing more productive
It is advantageous for persons using the cold rooms and growth facilities
to understand the basic principles involved in refrigeration systems.
Figure 1 shows the main components in a simplified system which consists
of a pump, condenser, receiver to store liquid refrigerant, expansion
valve, and evaporator.
(cooled by water
or air + fan)
Figure 1: Basic refrigeration system.
- 9 -
Provision for thermostatic temperature control of the space to be
refrigerated is included in working systems. Such systems have a dryer
to prevent any water vapor from freezing inside the system and plugging
it with ice. Other protective devices and refinements are usually
The pump or compressor compresses the refrigerant gas. As it does so the
gas warms up. The hot gas under high pressure is passed through the
condenser where it is cooled and condensed into liquid. Cooling of the
gas is achieved by circulating cold water or cold air around the outside
of the condenser coils. The chilled refrigerant liquid under pressure is
stored in the receiver until it passes through some type of control
mechanism (commonly an expansion valve) which sprays it in the form of
liquid droplets into the evaporator coil in which the compressor
maintains a low pressure.
The liquid refrigerant evaporates in the evaporator and the resulting gas
expands owing to the low pressure. Both evaporation and expansion
require that the refrigerants absorb heat and this results in a drop in
temperature in the evaporator. The evaporator is situated in the space
to be cooled or in an air duct supplying cold air to the space to be
cooled. The compressor evacuates the cold refrigerant gas from the
evaporator, compresses it, and passes it on to the condenser to repeat
the cycle. The physical properties of the refrigerant gas place
constraints on the temperature range over which it may be used for
refrigeration: R 12 works easily down to -20°C but can be used to -30°C;
R 22 works easily down to -30°C but can be used to -40°C; R 502 works
easily down to -40°C but can be used to -50°C; R 292 (propane) + R 503
(freon) work well from -50 to -130°C when used in a cascade refrigeration
In practice, the temperature of the evaporator coil must not vary too
much or else the air temperature in the cabinet cannot be held constant.
In order to achieve this, some hot compressed gas is bypassed from the
pump directly into the evaporator. The evaporator temperature is
controlled by regulating the cycling of hot gas and cold refrigerant.
In most working cold rooms the evaporator removes heat from the air in
the cold room. The system is thermostatically controlled to keep the air
in the cold room within a specified temperature range. When warm
material is moved into the cold room, heat flows from the warm object to
the room air to the evaporator. This means that the air temperature in
the room rises. As long as the amount of material moved into the room is
small or the temperature of the material is only a few degrees above room
temperature, the rise in air temperature will be small. However, if a
large amount of material at room temperature is transferred into a low
temperature room, the air temperature in the cold room will rise several
or even many degrees above the set temperature. The air in the room will
remain above normal until most of the heat in the material has been
transferred by convection to the evaporator. Rate of heat transfer will
depend on the specific heat of the air (a fixed quantity) and the rate of
air movement. If a large amount of warm material is moved at once into a
cold room, the air temperature in the room will remain above normal for
several hours. Where accurate control of the room temperature is
required, these effects must be avoided either by prechilling the
materials to be placed in the room or by moving in small amounts of the
material at suitably spaced intervals.
Moving large amounts of cold material into a warm room will produce
similar effects except that the room temperature will fall rather than
rise. If very rapid chilling is required, the evaporator coil may be
connected to a metallic plate. The material to be chilled is placed on
the metallic plate which conducts heat from the material to the
evaporator without the need for convection currents in air. Such a
system is of no advantage if a whole room is to be chilled.
Controlled temperature rooms are usually sealed to reduce leakage of warm
or cold air into them from the environment and they are insulated to
reduce heat transfer through the walls and doors. This makes possible
much better temperature control within the room and reduces the power
required to maintain the room temperature. Room doors should be kept
closed as much as possible.
Because the rooms are sealed dry ice (solid carbon dioxide) and liquid
nitrogen should never be stored in an enclosed cold room. Both these
materials will vaporize and the level of carbon dioxide or nitrogen in
the room will rise. If the level of carbon dioxide rises above 10% it
will cause persons exposed to it to become unconscious. In a cold room
this can result in death either by poisoning or hypothermia. High levels
of nitrogen result in asphyxiation and death.
In order to chill a cold room or growth cabinet to a temperature below
the freezing point, it is necessary to chill the outer surface of the
evaporator coil to a temperature below 0°C. Under such conditions any
water vapor in the cold room will be deposited as frost or ice on the
evaporator and will build up to the point where it plugs the evaporator
and stops air flow through it. Room temperature will then rise because
convective cooling has been cut off.
In practice, because water freezes at 0°C cold rooms cannot be maintained
indefinitely much below 4°C with a single evaporator if really accurate
temperature control is required. This problem is aggravated in a growth
room or growth cabinet where energy must be added as light during at
least part of the daily cycle. The best solution to this problem for
research purposes is to use two evaporators. One is used to cool the
room while the other is isolated from the room and warmed either
electrically or by hot gas from the refrigeration system. This heating
removes the frost and ice. This system is expensive and requires a
system of mechanical dampers to isolate the evaporator being defrosted.
It is, however, the only system that will provide accurate temperature
control below 4°C in cold rooms. It is also the only system that can be
used in growth cabinets if plants are to be grown under continuous light
at low temperatures and if air temperatures are to be maintained
accurately at temperatures below 5°C. In cold storage rooms where brief
(up to 15-20 minutes) warm periods can be tolerated, a single evaporator
may be used. When this evaporator coil is defrosted, air circulation is
- 11 -
cut off to the room. This system works well for cold temperatures near
and just below the freezing point, but below -15°C it rapidly becomes
unsuited to research needs as the temperature rises during defrost become
progressively bigger and longer. With single coil systems the frequency
and duration of defrosting is controlled by:
(1) the amount of moisture to be introduced into the system with the
material to be refrigerated,
(2) leakage of water vapor into the room from a door opening or into
the growth cabinet from the ambient air through cracks and seals
around the doors (growth cabinets cannot be air-tight or carbon
dioxide levels would fall too low for plant growth) , and,
(3) the design of the evaporator coil and refrigeration system.
Good design makes possible several days of sub-freezing operation for
application of cold stresses to test the hardiness of cold hardened plant
material. For such work, excellent room design is also needed to prevent
the development of layering of the air (producing a temperature gradient)
and cold spots within the room. Cold hardened plants are extremely good
thermometers and will react to temperature differences of as little as a
few tenths of a degree C.
Temperature control is an important feature of a controlled environment
facility. Several devices are used for temperature measurement and these
differ considerably in speed of response. A measuring device with slow
response time may show a greatly reduced range of fluctuation in
temperature in an environment with rapidly varying temperature. For
example, the apparent magnitude of the high temperature spike occurring
during defrost in a low temperature cold room lacking a dual evaporator
will be greatly reduced while its duration will be increased as the speed
of response of the temperature-measuring device decreases.
Of the devices used for temperature measurement, liquid bulbs (e.g.,
glass-alcohol or glass-mercury thermometers and some of the older style
chart recorders) and bimetallic strips have slow response times. Their
use tends to conceal the poor temperature control of cold rooms operated
below -15°C without dual evaporators. Well designed thermistors have
much better response times but have a linear response to temperature only
over narrow temperature ranges. This problem can be overcome by proper
electrical circuitry. Resistance bulbs (resistance wire wrapped around
ceramic) can be designed with moderate response times and are useful
where it is desirable to average a rapidly fluctuating temperature.
Thermocouples (especially ones made with very fine wire) have rapid
response times. For best results, the actual thermocouple and a length
of lead wire should be in the same temperature environment. This reduces
the heat conduction between the environment of the leads and the actual
junction. This precaution increases accuracy when the leads must pass
through environments with widely differing temperatures. Thermocouples
work conveniently with chart recorders, digital displays, dataloggers,
- 12 -
The description and measurement of light provided to plants present
special problems. Light is radiant energy in a certain portion of the
electromagnetic spectrum. For the present purposes it encompasses
radiation with wavelengths from 290 mu to 850 mu, those wavelengths
that affect plant growth. Different groups of wavelengths provide the
energy for different processes within the plant. Some of these processes
have been little studied. As a result, investigators cannot be sure of
what should ideally be measured.
The most important process in plants requiring light is photosynthesis,
which is responsible for providing the energy required for plant growth.
In higher plants, chlorophylls a and b are the pigments that absorb
the light for photosynthesis. These pigments absorb in the blue and red
portions of the spectrum. Among angiosperms, the synthesis of the
chlorophylls and of the chloroplasts themselves is light-dependent. Both
light intensity and quality appear to be involved in regulatory effects.
The conversion of protochlorophyllide to chlorophyllide a is
light-dependent in the angiosperms (absorption bands in blue and red).
Phytochrome is another important plant pigment system. It is involved in
the regulation of plant growth, especially in seed germination in some
species, dormancy in woody plants, and in the photoperiodic control of
flowering. The pigment exists in two interconvertible forms. One form
absorbs in a band around 660 mu (P r ) and the other in a band around
730 mu (Pp r ). Pp r is slowly converted into P r in the dark. It is the
proportion of these two forms in the plant that determines the growth
responses of the plant. The proportion and timing of application of
these wavelengths in the diurnal cycle are therefore important in
regulating plant growth.
Plants also contain other pigments such as flavins and carotenoids that
absorb light in the blue end of the spectrum. Phototropism is one system
activated by such light. The pigments involved have not been identified
with certainty. Other light-sensitive systems may exist and may be
detected by comparing plant growth responses in the field with those in
the greenhouse or growth cabinet.
Light intensity and total energy received per day are also known to
affect plant growth. Responses known as HER or high energy responses
occur, but little is known about them except that high light levels are
required for their initiation.
Day length, the proportion of the normal 24 hour day in which light is
supplied, is also very important in regulating rate of development of
many species. The phytochrome system is involved in those responses.
The multiplicity of light-sensing systems in plants greatly complicates
the already difficult problem of measuring the light supplied to the
- 13 -
Three units developed for different purposes are in common use for
measurement of incident light energy. These are the lux (1 lux = 0.093
foot-candles), the microeinstein per second per sguare meter (uE sec - ^-
m~ 2 ), and the watt per square meter (W/m 2 ).
The lux (1 lumen per square meter) and foot-candle (1 lumen per square
foot) were units developed by lighting engineers to measure illumination
for situations in which the ultimate light receptor is the human eye.
The standard human eye is most sensitive to yellow light of 555 mu.
Equipment for measuring illumination is readily available. However, some
of it is not very accurate.
Measurements of illumination have been criticized by plant scientists
because the spectral responses of the human eye and plants are not
similar. However, the same criticism applies to both the other units of
measurement of incident light (uE sec -1 m~ 2 and W/m 2 ) since neither of
these units evaluates the energy from different wavelengths in the same
way as a plant does. The only inexpensive solution to this problem is to
specify exactly the light source used and to include data on voltage and
power. For fluorescent light, the phosphor should be specified (e.g.,
cool white, daylight, wide spectrum grolux, etc). If more than one
source is used (e.g., cool white fluorescent and incandescent), separate
data for each of the sources should be provided.
The microeinstein sec"-*- m -2 is a unit developed to measure photon
flux by scientists interested in photochemistry. Radiant energy
(including light as defined above) is considered to be made up of
discrete particles called quanta or photons. The energy of a photon
depends on its frequency (inverse of wavelength) according to Planck's
law (E = hv) where E = energy in ergs per sec, h = 6.62 X lO -2 ^ ergs
per sec (Planck's constant) and v = frequency in cycles per sec. A
consequence of this is that photons of different wavelengths or
frequencies carry different amounts of energy. One molecule can absorb
one photon at a time. Ideally, a condition seldom realized, if a gram
molecule (mole) of photochemically reactive substance absorbs 6.022 X
10" (the number of molecules in a mole) photons or quanta of light, it
should become activated to produce a mole of product. An einstein is
6.022 X 10 2 ^ (Avagadro's number) photons, a sufficient number of
photons to activate 1 mole of photochemically reactive compound.
The watt/m 2 is the unit used by physicists to measure irradiance or
power per unit area.
Many workers use the term PAR or photosynthetically active radiation. It
measures the irradiation in the 400-700 mu waveband in W/m 2 or the
photon flux density in the same waveband in uE sec"^- m -2 . This
sort of measurement ignores the formative effects of different
wavelengths on plant growth.
The ideal solution to the problem of light measurement would be to
provide a plot of wavelength against incident energy to cover the whole
spectrum of interest for plant growth. This solution has serious
disadvantages in that the necessary equipment is expensive and reporting
of the results requires a table or graph.
- 14 -
Accurate interconversions among these units are complicated (see Appendix
14) and require accurate information about the spectral distribution
curve of the radiant energy from the source. Approximate conversions may
be made using empirical factors tabulated by McCree (1981), but such
conversions require a knowledge of the light source.
In practice, the maintenance of a nearly constant light level in a growth
cabinet requires constant monitoring. Light bulbs, both fluorescent and
incandescent, burn out. Ballasts for fluorescent lights fail. The light
output of fluorescent lights decreases with age. The drop is rapid
during the first 100 hours of operation and the rate of drop gradually
decreases subsequently. The ideal solution to these problems would be to
mount a photocell inside the growth cabinet and connect it to a recorder
or digital output.
The light output of fluorescent lights is temperature-dependent. It
drops off at high temperatures (above 35°C) and at low temperatures
(below 10°C). Since it is the actual tube temperature that is critical,
the limits for operation to provide adequate light output will depend on
air circulation around the lights.
For really critical work on light quality, the spectral distribution of
the radiant energy should be checked periodically. There have been
reports of changes in the spectral distribution of output from at least
some of the more specialized fluorescent lights.
Control of the amount of water vapor in the atmosphere of a growth
cabinet is important because it influences the transpiration rate of the
plants in the chamber. Transpiration rate is partly determined by the
difference between the water vapor pressure inside the leaf and that in
the ambient air, assuming that air circulation around the leaves is rapid
enough to prevent the formation of a layer of air surrounding the leaves
with a relatively high vapor pressure. The vapor pressure within the
leaves will normally be close to that of water at the same temperature.
The vapor pressure of water rises rapidly as the temperature rises.
Relative humidity is the amount of water vapor in the air expressed as a
percentage of the maximum amount of water vapor that the air could hold
at the given temperature. Since the water vapor holding capacity of air
rises with temperature, a rise in temperature of the air will cause a
drop in relative humidity if the absolute amount of water vapor in the
air remains constant. This explains why, in a growth cabinet with rapid
temperature cycling (hunting), comparable rapid cycling of relative
humidity occurs. The relative humidity will drop as the temperature
rises and rise as the temperature drops.
Four general methods are available for measuring relative humidity.
First, there is determination of dew point. This type of method
determines the temperature at which the air is saturated with water
vapor. It is accurate but rather expensive. It may be used to monitor
- 15 -
conditions in a growth cabinet. Second, there are the wet and dry bulb
thermometers, thermocouples, or thermistors. These measure the maximum
temperature drop that can be caused by evaporative cooling in the
atmosphere. Relative humidity is then determined from tables (Weast et
al. 1985-86). This technigue can be used for measuring or monitoring the
relative humidity in a growth cabinet. It is accurate and works well as
long as the wick on the wet bulb sensor can be kept fully moistened with
pure distilled water. The third group of methods depends on the change
in physical properties (e.g., length of hairs, or electrical resistance
of hygroscopic salts such as LiCl) of materials as the relative humidity
of the surrounding air changes. This type of unit reguires careful
calibration. Some units of this type are suitable for controlling and
monitoring humidity in growth cabinets. The fourth method for measuring
relative humidity is by infrared detectors. These are accurate but
expensive. They depend on measuring the quantity of water vapor in the
air by its ability to absorb infrared radiation of certain wavelengths.
Four methods for humidity control are available at Lethbridge:
refrigeration-reheat, chemical dryer, additive, and plastic bagging.
With properly designed equipment, refrigeration-reheat is an accurate
method for controlling humidity. It relies on removing excessive
moisture from the air by chilling the air in the evaporator coils. The
air temperature is then raised by introducing hot refrigerant gas into
the evaporator. Temperature control is achieved by proper cycling of hot
gas and cold refrigerant into the coil. The air to be chilled must be
moist enough that water will condense on the evaporator coils when the
air is chilled to the dew point. Proper evaporator design is also
necessary to make sure that all the air leaving the evaporator is at the
Chemical dryers are used where low relative humidities are required.
These use a hygroscopic chemical to remove water vapor from the air. The
chemical is usually regenerated by heating.
Additive humidity control is useful only when relative humidity must be
raised above the fairly dry conditions usually present in a growth
cabinet. A humidity sensing unit controls addition of water by a misting
or atomizing device or in the form of steam. Pure water (demineralized
or distilled) or steam (not containing fungicides, bacterocides, and pH
control chemicals often used to protect the condensate return lines) must
In plant disease research, relative humidity levels close to 100%,
sometimes with dew present, are often required for infection studies.
These levels can be obtained in growth cabinets by covering the plants
with plastic bags, preferably in the dark. In the light, difficulties
may be encountered with radiant heating. In a growth room this system
can be scaled up and a plastic tent and humidifiers can be used to permit
handling the large populations needed in plant breeding programs. It is
especially useful where temperature control is required for good
- 16 -
In controlled temperature rooms with minimum light (below 1 klx), it is
usually assumed that all points within the room are at the same
temperature. For critical work, this assumption should be tested by
simultaneous temperature measurements using thermocouples and a recorder
or datalogger of some type. The actual pattern of air movement within
the room will determine how closely this assumption is realized. Very
serious discrepancies (several degrees C) may occur in badly designed
rooms. Placement of large amounts of material within the room may also
affect patterns of air flow and temperature uniformity.
Operation of a controlled temperature room at the freezing point poses
special problems for biological research if the material must not freeze.
Experience at Lethbridge shows that moist soil or vermiculite exposed to
room air will freeze at air temperatures slightly above the freezing
point even though stoppered flasks of distilled water in the same room do
not freeze or supercool. This problem arises because the air movement in
the room, which is essential for temperature uniformity, causes
evaporation from the moist surface of the soil or vermiculite. Water
must absorb heat in order to evaporate. Thus, heat flows from the soil
or vermiculite to the water to facilitate its conversion from the liquid
to the gaseous state and, in the process, the soil or vermiculite is
chilled below the freezing point and the water in the medium freezes.
The chilling is maintained after the soil freezes because water vapor
continues to be formed by ice sublimation. Our solution to this problem
is to raise the air temperature in the room. For our rooms, a temperature
of 0.7 or 0.8°C is required to prevent exposed moist soil or vermiculite
from freezing. An alternate solution to the problem would be to cover
the surface to prevent the evaporative cooling.
Plant growth cabinets and rooms
INTRODUCTION The purpose of growth cabinets and growth rooms is to
provide controlled, reproducible conditions for plant growth. At first
glance it would appear that all that is required is to set the air
temperature, intensity and duration of lighting, and relative humidity.
For many experiments, reasonably reproducible results may be obtained by
doing this, provided that the plants are to be grown at 20 to 25°C and
that high light intensities and close humidity control are not required.
If plants are to be grown under conditions such that a small change in
conditions causes a measureable change in plant growth, then reproducible
results are difficult to achieve in growth cabinets. However, overall
trends can easily be detected but not quantified accurately.
We have not studied these problems extensively at Lethbridge but have
made some measurements that illustrate the magnitude and nature of the
problems that will be encountered. Part of the data comes from work on
cold hardening of wheat.
- 17 -
Under cold hardening conditions, rate of growth and length of leaves are
very sensitive to small differences in mean temperature. Furthermore, it
is probably true (Peacock 1975) that the apical meristem is the site of
temperature reception, at least for control of leaf length. The meristem
of young wheat plants is located below the surface of the growth medium.
Although we have not performed replicated or even repeated experiments on
the true microclimates, our experiences indicate the need for extensive
serious research into the problems to be encountered.
Temperature, light, humidity, air movement, watering, containers,
nutrition, carbon dioxide, other gases, media and nutrients, diseases and
pests will be discussed to the extent of our experiences. Temperature
and humidity are probably the most difficult to control. Good humidity
control reguires good temperature control. The temperatures experienced
by the aerial parts of the plant depend on several factors: air
temperature, air velocity, humidity, water status of plants, and light.
The temperature of the below-ground parts of the plant will depend on air
temperature, air velocity, watering, water content of growth medium,
light, and container configuration.
TEMPERATURE Measuring temperature in a cabinet where high levels of
light are supplied for part or all of the daily cycle presents special
difficulties because air movement is required to maintain temperature.
It is conventional to measure air temperature at a site which is
protected from the lights. In Conviron growth cabinets this is achieved
by removing a small stream of air from a central location in the cabinet
and passing it over the sensing unit, which is located in the machinery
compartment. If an exposed thermometer is mounted in a growth cabinet in
the light cycle, it will be observed that the temperature is higher
closer to the lights. This response is caused partly by radiant heating
of the thermometer and partly by air temperature. Plant leaves will
experience this effect and its magnitude will depend mostly on the
quality and intensity of the light supplied.
Although the aerial parts of plants are surrounded by air, they are not
necessarily at the same temperature as the ambient air. These
relationships and the measurement of leaf temperature are discussed by
both Salisbury and Tanner (see Tibbitts and Kozlowski 1979). Although we
have done no work in this area, a summary of the situation is useful.
Even if the air temperature is kept constant during the light and dark
periods, there is no reason to expect that the plants will experience a
constant temperature throughout the day. Plants will probably respond to
the temperatures of their parts rather than to the ambient air
temperature even though the latter will have a large effect on plant
temperatures. In the light period the leaves will absorb a considerable
amount of the energy radiated by the lights. This energy will be
converted to heat which will raise the temperature of the leaves. Since
the light intensity is not the same in all parts of a growth cabinet,
these heating effects will be uneven.
Many but not all plants open their stomata during the light period.
This serves two purposes. It allows uptake of carbon dioxide for photo-
synthesis and sugar manufacture and for evaporation of water for cooling.
This evaporation powers the transpiration stream for transfer of mineral
nutrients from the growth medium to the leaves. Since evaporation of
water reguires that the water molecules take up heat, evaporation will
cool the leaves. This cooling will be influenced by a number of factors,
some of which vary among plant species. These factors include:
(1) internal leaf structure and abundance of stomata,
(2) whether stomata are open or closed (controlled chiefly by light
and water status of the plant),
(3) water vapor pressure gradient between air in the interior of a
leaf (usually close to saturation) and exterior air. This
gradient will be influenced by relative humidity of ambient air
and air movement over the leaf surface,
(4) temperature (higher temperature means higher transpiration),
which changes water vapor pressure gradient and affects stomatal
(5) water status of plants, which is affected by availability of
Orientation of leaves will affect the amount of radiant energy and
consequently the leaf temperature. As the plants grow, additional leaves
will be produced and these will usually shade the lower leaves thereby
reducing the light energy that they receive and consequently their
During the dark periods it is to be expected that leaf temperatures and
air temperatures will be similar except in those species (e.g., succulents)
with stomata open at night and those with a cuticle so thin that appreciable
water loss occurs through the cuticle. Where appreciable water loss
occurs from leaves in the dark periods, leaf temperatures will be below
air temperatures because of evaporative cooling.
Some factors that influence the temperature of the growth medium are
container geometry, radiant heating, evaporative cooling, moisture
content of growth medium, watering, cycling of air temperature, and size
One of our first experiences with these problems involved container
geometry. Wheat was being germinated and cold hardened at a constant 2°C
under a 16 hour day of approximately 16 klx, provided by cool white
fluorescent tubes plus a small incandescent supplement, in a vermiculite
medium watered three times a week. Some of the plants were growing from
seeds sown approximately 1 cm deep in wooden flats 25 x 39 x 9 cm filled
to a depth of 7 cm with vermiculite. The others were growing in the same
medium with the same watering schedule in green plastic pots (top
diameter 15 cm, bottom diameter 10.3 cm, height 14 cm) beside the flats
in the same growth cabinet. Plants in the plastic pots took 2 weeks
longer to emerge. Crown temperatures in the plastic pots were not
checked but were probably colder.
- 19 -
Moist soil surfaces may be chilled by evaporative cooling in the dark
period or, if heavily shaded, by the plant canopy. During the light
period, exposed soil surfaces are warmed by radiant heating.
If the plants are watered with nutrient or distilled water that is much
warmer or colder than the temperature of the growth medium, then the
temperature of the medium will rise or fall respectively. This
disturbance will persist for several hours (Fig. 2). Properly chilled
water or nutrient for watering cannot be produced by storing it in the
growth cabinet in which the water or nutrient is to be used as long as
there is a light period in the cabinet. Under such circumstances,
radiant heating will warm the nutrient.
In a growth cabinet with an air temperature of 7°C and continuous light
of 21.5 klx supplied from cool white fluorescent plus incandescent light,
several temperature measurements were made. The temperature of nutrient
in an unshaded carboy was 15.5°C. The temperature (mercury thermometer
calibrated at 0°C with ice-distilled water) under an empty (no plants)
flat of vermiculite was 7.3°C, on top of the flat it ranged from 10.5 to
14.5°C (exposed), and a thermocouple at about 1 cm depth showed 16°C. A
comparable flat containing a heavy canopy of 9-week-old wheat plants
grown at 7°C with continuous light gave a temperature of 9°C at plant
crown level (Fig. 2). This provides a dramatic example of the effect of
shading the surface of the medium on the temperature of the medium under
Similar shading responses and appreciable variability were observed in
experiments similar to the above except that the air temperature was
maintained at a constant 3°C (under 21.5 klx of continuous light). A
flat with 4- to 5-week-old seedlings showed crown temperatures of 7°C.
Differences in crown temperatures of 2 to 3°C have been observed in
plants grown in flats under apparently similar conditions. Differences
in plant growth have been noted under these conditions.
Figure 2. Effect of watering with nutrient at 20°C on crown temperature
of 9-week-old plants grown in medium grade vermiculite in flats 25 x 35 x
9 cm filled with 7 cm of vermiculite. Plants were grown at a constant
temperature at 7°C under 21.5 klx of cool white plus incandescent light
For a proper study of leaf length (a trait correlated with cold
hardiness) of wheat grown under cold hardening conditions, these
temperature aberrations will have to be controlled. One requirement will
have to be that nutrient or water used for watering is prechilled in a
dark cold room run at the proper temperature.
Figure 3A shows data on crown temperatures of wheat plants being cold
hardened under a regime frequently used at Lethbridge. This regime
provides 8 hours of darkness at an air temperature of 4°C and 16 hours of
9.7 klx of cool white fluorescent plus incandescent light with an air
temperature of 6°C. Minimum dark-period crown temperatures approximated
minimum air temperatures but maximum light-period crown temperatures were
4°C higher than maximum air temperatures. The evaporative cooling effect
in the dark was not detected and was probably relatively small in this
test, but radiant heating effect was quite large (4°C).
- 21 -
Figure 3. Plant crown temperatures during a complete temperature and
light cycle; _ _ _ _, programmed temperature; , temperature of
crown depth; t p m , temperature of crown depth in flat with no
A. Flats with plants growing under 24-h period with 8:16 h and 4:6°C
light:dark, and 8-10 klx cool white fluorescent plus incandescent light,
B. Flats under 6-h period with 4:2 h and 2:20°C, and 27 klx cool white
fluorescent plus incandescent light.
- 22 -
In studies on days to head of wheat grown at a constant 20°C under 16
hours of 21.5 klx of cool white fluorescent plus incandescent light,
growth response problems have not been observed although similar types of
temperature discrepancies occur. For example, in pots (1 gallon black
plastic, diameter 15 cm, height 17.5 cm filled with soil) exposed to 20°C
with no plants, the day temperature at 2.5 cm depth in soil was 23 °C and
the night temperature was 20°C. The changes in temperature under these
conditions occurred over about a 2-hour period. In comparable pots with
a good plant growth, the day and night temperatures were 21 and 20°C
respectively. An exposed (i.e., not shielded) thermocouple in the plant
canopy recorded 23°C in the light cycle and 20°C in the dark. The change
from light to dark values occurred in a few minutes. If the pot was
watered with tempered water (water at the temperature of the cabinet) in
such a way that all water was applied directly to the soil surface, the
temperature in the plant canopy changed little (ca. 1°C) . If, however,
the tempered water was sprinkled over the plant canopy, the temperature
(exposed thermocouple) in the plant canopy fell from 23 to 20°C. The
drop occurred over about 1.5 hours and had not recovered to 22°C until
about 2 to 2.5 hours later. This behavior is the result of evaporative
cooling induced by moisture on the thermocouple or the nearby leaves.
Although we realize that exposed thermocouples should not be used to
measure temperatures in high levels of light, nevertheless the plant
leaves are exposed and radiant heating is one of the factors affecting
leaf temperature. Further, we should realize that a plant leaf will
respond to the leaf temperature rather than to the air temperature.
For a plant such as wheat, which possesses an underground growing point
for several (spring types) to many (unvernalized winter types) weeks, the
interpretation of experiments using large daily temperature changes is
difficult. Figure 3B provides actual temperature data from crown depth
in a flat of vermiculite with no plants and a flat with plants from an
experiment in which a 6-hour temperature and light cycle was used. Under
these circumstances, the daily temperature range is smaller under a plant
canopy than in a flat without plants and the maximum and minimum
temperatures are 6 and 8°C lower and approximately 4°C higher than the
maximum and minimum air temperatures, respectively. Discrepancies
between maximum and minimum air and crown-level temperatures were less
when the length of the cycle was increased to provide 16 hours at 20°C
(light) and 8 hours at 2°C (dark). The rate of rise and fall of the
temperature at crown level after a change in air temperature was found to
be greater in a relatively dry flat (2 days after watering in a flat with
good plant growth) than in a relatively wet flat (shortly after watering
in a flat with good plant growth) . This effect was not noticed within 2
days in a flat of vermiculite with no plant growth.
It is assumed that water loss from a flat with good plant growth is much
greater than that from a flat with no plant growth. Thus, the plant
population in a container controls water levels in the medium and
consequently the exact pattern of daily cycling of crown level
- 23 -
LIGHT The irradiance over the growth area of a growth cabinet is not as
uniform as the air temperature. In the corners it may be only 80% of
that near the center. The conseguences of this may not be serious at
lower light intensities or normal (ca. 20°C) air temperatures. However,
at higher light intensities and low (1 to 10°C) air temperatures, the
lower light levels will result in lower effective temperatures (i.e.,
temperatures experienced by the plant) . Differences in growth rate and
morphology may be apparent.
Increases in the day length may cause changes in growth rates of plants
which are doubtless the result of changes in the effective temperatures.
For example, wheat sown and grown at 2°C under continuous 16.1 klx of
cool white plus incandescent light emerged in 11 to 12 days, whereas when
the air temperature was 3°C and only 16 hours per day of comparable light
was provided, emergence took 4 to 5 weeks. With an 8-hour day at 3 . 2 klx
at 3°C, emergence occurred after 6 weeks.
HUMIDITY For most of the research in growth cabinets at Lethbridge we
have not found humidity control to be necessary. When higher humidities
have been needed, they have been obtained by keeping water in the tray in
the floor of the cabinet.
However, for studies on water relations humidity control is essential.
If work on water content and cold hardiness is to be undertaken, special
difficulties will be encountered since dew points below freezing will
probably be needed.
AIR MOVEMENT Air movement has been reported to be a determinant of plant
growth but it has been little studied under controlled conditions.
Air movement will influence leaf temperature by increasing transpiration
and conseguently evaporative cooling. Air movement will also increase
the availability of carbon dioxide by preventing air stagnation around
Except for their effect on temperature, responses to small changes in air
movement seem to be quite small. However, under cold hardening
conditions (2 to 3°C with light), growth differences on two sides of a
growth cabinet with upward air flow have been observed. These have been
traced to differences in air flow on the two sides of the cabinet caused
by small differences in fan speeds between the two fans serving the sides
of the cabinet. Such problems have not been encountered with plants
growing at 20 to 25°C.
WATERING An adequate water supply is essential for plant growth.
Controlling the supply of water presents serious difficulties and the
available methods are limited because of the peculiarities of water
movement within soils and other plant support media.
- 24 -
The most satisfactory method of supplying water is to use a solution
culture (hydroponics). This technique requires that the roots be
immersed in a very dilute solution of mineral salts (see Fig. 4). For
many but not all plant species, the solution must be aerated by bubbling
air through it to supply sufficient oxygen for healthy root development.
The water lost by transpiration has to be replaced, as do the mineral
salts taken up by the plant. This can be done manually by changing the
nutrient solution at frequent intervals (frequency increasing as the
plants grow) or by an automated system that replaces both water and salts
taken up by the plants. Automated systems require frequent monitoring to
ensure that no malfunctions have occurred.
Sand or gravel culture methods are also satisfactory if the system is
carefully designed and operated. Watering with nutrient solution can be
done from above or below. Watering from above is usually more
satisfactory in growth cabinets. It is accomplished by allowing nutrient
to drip on to the upper surface of the medium from tubing (plastic
preferred) with regularly spaced small holes. Large-bore tubing, careful
levelling of the system, and careful checking of hydrostatic pressures
and flow rates are needed to ensure uniform watering. Flow rates must be
great enough to prevent excessive salt accumulation in the medium as this
will injure the plants. Facilities for drainage are necessary. Watering
from below is achieved by periodically pumping nutrient up through an
opening into the bottom of the container and allowing it to drain out.
An overflow must be provided to control the maximum depth of nutrient in
the container in each cycle. Large-bore tubing must be used and the
system carefully checked to ensure that rate of nutrient flow into and
drainage out of each container are similar. If this is not done,
watering and growth will not be uniform from one container to another.
Both systems of sand or gravel culture may be partially or completely
automated. They should be monitored frequently and regularly to check
for proper operation. For work between and 15°C and at high
temperatures above 30°C, tempered nutrient should be used to avoid the
root and crown temperature effects described elsewhere.
Where levels of precision are satisfactory, manual watering with nutrient
from a hose or watering can may be used.
If careful control of plant nutrition is not necessary, plants may be
grown in fertile soil and watered with tap water from a hose. Tempered
tap water is preferable, especially in areas where the tap water may be
cold (below 10°C) for part of the year.
Studies on the responses of plants to prolonged water shortages when
grown in soil present special problems which arise from the behavior of
the soil water system.
- 25 -
1 quart plastic container with
sides painted green ( to
prevent algae growth in
removable waxed wood
Figure 4. Containers used for solution culture of cereals at Lethbridge,
- 26 -
Two rather imprecise terms, field capacity and permanent wilting point,
are often used by plant physiologists to describe the water status of a
soil. At field capacity (water potential usually above 30 kPa) the soil
contains the maximum water content possible without drainage of water
occurring from it under the force of gravity. At the permanent wilting
point (usually -1000 to -2000 kPa) plants will wilt and remain wilted
even when transpiration ceases. Both these "constants" are affected by
soil type and the latter is affected, in part, by the test species of
plant that is used.
In addition to water vapor, water in the soil exists in the following
(1) adsorbed on soil particles; this form requires large forces to
(2) held by surface tension in the capillary pores in the soil,
(3) free water in the large pores. The latter is the only category
that moves under the influence of gravity alone. When all large
pores are full of water, the oxygen supply to the roots is very
poor and only plants adapted to such conditions will grow
Except in soils completely saturated with water, water movement in soil
is chiefly along a water potential gradient (i.e., gravitational forces
are unimportant) . In the field, the chief force drawing water down to
lower levels is derived from the low water potential of the drier soils
at those levels. In the bottom of a well watered pot with drainage
holes, such lower levels of dry soil do not exist, so the water potential
at the drainage holes is near kPa and water tends to accumulate in the
bottom of a pot and slowly drain out under the influence of gravity.
This results in a waterlogged layer in the bottom of a well watered pot
When dry soil is moistened with water, the water is adsorbed on the soil
particles and the capillary pores fill with water before there is any
free water that can move readily in the soil. This means that when soil
is watered the water content must rise to field capacity before much
water movement occurs. So, in a pot being watered there is a sharply
defined front between the dry and wet soil (at field capacity). It is
therefore not possible to water a pot full of uniformly packed soil and
end up with a pot full of uniformly wet soil with a water content below
that of field capacity. When a pot of uniformly dry soil is watered, the
end result is either a pot full of soil at field capacity or a pot with
an upper layer of soil at field capacity and a lower layer of dry soil.
If the soil in the pot is caked or crusted, free water may flow to lower
soil layers down cracks or down the inside of the sides of the pot.
The usual way of controlling water in plants grown in soil for studies of
drought tolerance is to water the pots to field capacity, weigh the pots,
and add water as soon as the water content falls to a certain predetermined
level. This produces an environment with a fluctuating water supply to
- 27 -
In a pot with growing plants the situation is somewhat different. Roots,
which are usually not uniformly distributed, can lower the water
potential in the soil to the permanent wilting point. Thus, roots tend
to produce a region of dryish soil (between the permanent wilting point
and field capacity) around them. Adequate watering raises the moisture
content back up to field capacity.
CONTAINERS Container size, shape, and color should be standardized.
Container size can influence the required frequency of fertilization if
soil is used as a growth medium. As the nutrient supply in small
containers will be depleted sooner than in large containers, symptoms of
mineral deficiencies will appear sooner in small containers. The color
of the containers may affect soil temperatures as a result of the
container's ability to absorb light energy during the light cycle. Clay
pots can produce two side effects. The clay walls adsorb nutrients and
later release them by processes similar to those exhibited by soil
particles. The walls of clay pots are porous so that moisture from the
soil diffuses through them and evaporates from the surface. This will
cool the pot and its contents. Container geometry can affect the
temperature of the medium as discussed in the section under temperature.
NUTRITION AND MEDIA Ten elements (macronutrients) are required in
moderate to large amounts for plant growth. Water supplies hydrogen and
oxygen. Carbon dioxide in the air supplies the carbon. The
others--calcium, magnesium, nitrogen, phosphorus, potassium, sulfur, and
iron — are supplied by the soil. In addition, six elements (boron,
chlorine, copper, manganese, molybdenum, and zinc) are required in trace
quantities (micronutrients) . Halophytes require sodium. Cobalt is
required for the symbiotic fixation of nitrogen by legumes. Excessive
quantities of the micronutrients and most macronutrients can be toxic.
If nutrients are supplied to sand or gravel culture containers from
above, either from watering cans or by drip irrigation, care must be
taken to supply sufficient nutrient to flush excess salts from the medium
or salts will build up and may become toxic.
The nutrient solution most often used at Lethbridge is a modification of
Hoagland's No. 1 (see Appendix 13) with the iron supplied as iron
citrate. Because use of ferrous sulphate resulted in iron deficiency
symptoms in wheat, iron citrate recommended by Hewitt (1952) was used
instead. It is satisfactory but troublesome to dissolve.
Three growth media are used at Lethbridge. These are soil, Cornell mix
(see Appendix 12), and vermiculite. The history of the soil in use at
Lethbridge Research Station has been known since 1906. It was obtained
from the headland of one of the Research Station experimental areas when
a road was widened. No pesticides or fertilizers had been used on the
land and it had been sown to grass for many years. The soil was collected
several years ago and is expected to last another 15 to 20 years.
When it was available, a fine (No. 5 or plaster aggregate) grade of
vermiculite was the most satisfactory. No. 3 or medium grade vermiculite
is now being used. Seed is sown directly into dry vermiculite. As a
precaution, we find it necessary to wash the vermiculite thoroughly with
distilled water when the seed is moistened. This serves to flush out
some unidentified water-soluble toxin that has been found occasionally in
the vermiculite we use. The toxin prevents seed germination and results
in wheat plants with short dark green leaves.
CARBON DIOXIDE Carbon dioxide is the substrate for photosynthesis and by
far the most important carbon source for green plants. It is freguently
the limiting factor that controls the rate of photosynthesis. Two other
potentially limiting factors are light and temperature. When carbon
dioxide levels fall to low limiting values they control the rate of
photosynthesis, and increases in light and or temperature will have
little or no effect on the rate of photosynthesis. Because of their
effect on the rate of photosynthesis, changes in CO2 levels will affect
growth rate. There are reports in the literature suggesting that CO2
may have additional biochemical and morphological effects on plant growth
Carbon dioxide levels in the atmosphere have been gradually rising. It
is believed they were around 275 ppm before the industrial revolution.
By 1900 they had risen to approximately 290 ppm, by 1960 to 320 ppm, and
by 1976 to close to 330 ppm. They are thought to be increasing at around
0.7 ppm per year at present. They tend to rise in winter and fall in
summer due to photosynthetic uptake by plants. The annual range is
around 6 ppm.
Human activity affects local CO2 levels. Levels are high in large
cities with lots of human activity and oxidation of fossil fuels and low
in the rural areas, especially in summer. In houses and office buildings
they rise to 600 ppm. Levels of carbon dioxide above 2% may cause toxic
symptoms in plants if they persist for long periods of time.
In a sealed growth cabinet, CO2 levels will fall rapidly during the
light cycle. C-4 plants like corn can lower CO2 levels in the light
cycle to 50 ppm and C-3 plants like cotton can produce C0 2 levels up to
150 ppm. The presence of an investigator in a walk-in growth room may
raise the CO2 levels to between 500 and 600 ppm. During the dark
cycle, CO2 levels will rise due to plant respiration.
Prevention of large changes in C0 2 concentration will require
impractically great rates of air exchange between outdoor air and growth
chamber air. Such exchanges are theoretically calculated to be as high
as 75% of chamber volume per minute. Exchange with ambient air may cause
problems if there is much human activity in the room surrounding the
plant growth room (high C0 2 ) or if there are many plant growth chambers
in the vicinity (low C0 2 if all lights are on at the same time).
- 29 -
Commercial plant growth cabinets have provision for exchange of outside
air. Such provision, however, falls short of that required to maintain
CO2 levels in a cabinet full of large, rapidly growing plants. To some
extent this is compensated for by the fact that most commercial cabinets
are not very air-tight, a fact attested to by the problems of maintaining
low humidities inside them.
Controlled additions of CO2 (free from compressor oils) to the growth
cabinet atmosphere are the best way to control C0 2 levels in the light
cycle. Removal of excess CO2 during the dark cycle poses greater
problems and there is not universal agreement on a satisfactory method
for achieving this.
Control of CO2 levels requires monitoring. The most accurate method of
determining CO2 is with an infra red gas analyzer. This equipment is
expensive and requires careful operation if accurate data are to be
obtained. A cheaper system is based on the fact that, as CO2
concentration in distilled water increases, so does electrical
conductivity. The air to be analyzed is bubbled through water which is
then passed through a conductivity cell. Both of these methods may be
connected to an automated system for additive control of CO2 levels.
OTHER GASES The control of oxygen levels is not normally required in
growth cabinets studies, even though modified levels are used
commercially for fruit storage and ripening.
Sealed growth cabinets may be used for study of air pollutants. With
such units it must be remembered that plants, especially those with
ripening fruits, give off ethylene, a plant growth regulator causing
epinasty and accelerating leaf fall and fruit ripening. With very
sensitive plants it may be necessary to filter the ventilating air to
remove air pollutants. The topic of pollutants is not under investigation
at Lethbridge and its detailed discussion is outside the scope of this
DISEASES AND PESTS The discussion of diseases and pests will be confined
to those diseases and pests which are or have been a problem in the
Phytotron and greenhouse at Lethbridge. The problems are to some extent
determined by the crops that are grown and by the diseases and pests
prevalent in the outdoors.
The most important aspect of disease and pest control is prevention.
In practice, this means sanitation. Sanitation is the biggest problem
Normal growth cabinet operation usually involves completely removing one
crop before the next one is planted. If the cabinet is left empty for a
week or two, or if a very high temperature is maintained for a shorter
period of time, the pests will be eliminated. Leaving the cabinet empty
allows time for preventive maintenance of the refrigeration equipment and
permits thorough cleaning. The first step in cleaning is to remove all
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plants and plant debris, followed by sweeping and vacuuming. Then the
growth cabinet floors are removed and soaked overnight in "Lime-a-way" (a
commercial descaling preparation with phosphoric acid as the active
ingredient), and later rinsed with water. The tray under the floor is
vacuumed and rinsed. If the tray is heavily crusted with salts,
Lime-a-way is used to remove all scale and dirt. Finally, if necessary,
the cabinet walls are washed with soap or detergent.
Care is taken to avoid introducing diseased or insect-infested plants
into the clean cabinets. Since we have a large operation, greenhouse
staff on weekdays can be assigned to look after specific areas. This
reduces the chances of a pest or disease moving from one area to another
(e.g., from greenhouses to growth cabinets) on staff clothing or bodies.
Cabinet doors are kept closed as much as possible since many of the
problems enter through the doors and spread out from the areas around the
Greenhouse sanitation is a much greater problem largely because there is
such a temptation not to clean out all the plants from a greenhouse
compartment or room at one time. Even a few plants under the benches can
harbor small residual populations of the more troublesome pests. For
best results, expanded metal rather than wooden bench tops are used.
Gravel floors have been replaced with concrete. Both these changes have
reduced our pest problems. Between experiments, all plants and plant
debris are removed from a greenhouse compartment or room. The floors,
including all corners and areas under the benches, and the metal tops are
flamed with a propane weed burner if there has been a pest or disease
problem and usually a very high temperature is maintained for two or
three days to eliminate the pests.
Most greenhouse pests come in from outdoors. The entry of some of these
can be prevented by screening the openings. Air introduced in the summer
through the swamp coolers is filtered of pests that might enter with the
incoming air. The positive pressure built up in the greenhouse also
helps prevent the entry of diseases and pests.
Powdery mildew (Erysiphe sp.) is a problem on cereals and some other
crops in the greenhouse and growth cabinets. It produces small, white,
powdery lesions on the leaves and stems. It tends to be more serious
under conditions of low light in the winter in the greenhouses. Spread
is rapid. Problems in growth cabinets develop on older plants, probably
because the growth cabinets are cleaned before seeding and it takes time
before the disease is introduced into the cabinet. It is uncommon on
cereals under hardening conditions, probably because of the low
temperature. Spraying with Bayleton is the best method of control in a
growth cabinet. Fine sulfur dusted over the plants works well in a
greenhouse, but sulfur is too corrosive for regular use in a growth
Damping off (caused by one or more of several fungi including Pythium,
Rhizoctonia, Fusarium, and Phytophthora spp.) is sometimes a problem,
especially when seeds are planted deep. It does occur in the
greenhouse. Where Pythium is the chief problem, proper watering is
- 31 -
important. Plants must not be allowed to dry out too much nor should
they be overwatered. Captan or other seed dressings can be used as a
fungicide for partial control. Soil sterilization is sometimes
recommended but a sterile soil is an excellent medium for growth of fungi
that cause root diseases because sterilization removes competing
Rusts have not been a problem because the climate of the Lethbridge area
is too dry for a rapid buildup in most years.
Healthy seed is used to reduce seed-borne diseases.
In general, the use of persistent systemic insecticides and miticides is
avoided for control of pests. Some of these systemics are quite toxic to
humans, a property shared with many other insecticides and miticides. In
an institution like ours, where entomological research is carried out,
care must be taken, especially with persistent systemics, to avoid
contamination of the phytotron and greenhouses since some scientists use
these facilities for studying insects.
The greenhouse staff have been trained in using pesticides. They wear
proper protective clothing when applying pesticides. Treated areas are
sealed off as far as possible and posted with necessary warning signs.
The two-spotted spider mite, Tetranychus urticae, is a serious
problem. Mites usually feed on the underside of leaves by sucking the
plant juices. They produce small, pale-colored spots lacking the tiny
black spots characteristic of thrip damage on leaves. They may be seen
and identified with a magnifying glass since they have eight legs,
whereas adult insects have only six legs. In a growth cabinet, they are
controlled by spraying with Pentac, Kelthane E, Morestan, and Vendex 50 W.
In the greenhouse, fumigation with Plantfume 103, DDVP, or Tedion is
satisfactory. These compounds are too toxic to humans for use in a
growth cabinet or growth room.
Various species of aphids are a problem because they suck plant juices,
may transmit virus diseases, or inject toxins into plants. Aphids have
six legs and are usually present in a wingless form. However, most
species have at least one winged form in their life cycle. Fumigation
with nicotine is effective in the greenhouse. In a growth cabinet or
growth room, one or two sprayings with Pirimor is sufficient for control
in a cereal, canola (rape), or saf flower crop.
Thrips are tiny insects that suck plant juices. Their presence is
indicated by small pale spots on the leaves. The spots are associated
with tiny black dots (feces) which help differentiate thrip infestations
from mite infestations. Fumigation with nicotine or Plant Fume 103 gives
good control in the greenhouse. Spraying with orthene works in the
growth rooms and growth cabinets.
- 32 -
Whitefly, Tcialeurodes vaporariorum, used to be a problem in the
greenhouse, especially on beans. They have not been a problem in growth
chambers and growth rooms. With the introduction of all the sanitation
methods described above, whiteflies have been largely eliminated from the
greenhouses. They may be controlled by spraying with Ambush.
Mealybugs also were a problem. They are flattened oval insects, usually
without wings, 3 to 7 mm long and covered with a white powdery wax. They
have been eliminated from our greenhouses by sanitation procedures.
Fungus gnats or manure flies (Platyura sp. and Sciara sp.) occur
occasionally and are controlled by malathion drenches.
Algae can cause problems. They will grow in the nutrient solutions used
for watering. Such solutions must be kept in the dark or covered with
green garbage bags to exclude the light. Although they grow on the
surface of media at cold hardening temperatures (i.e., to 10°C), they
have not caused problems. Sanitation of cabinets prevents serious
Mice are a recurring problem, mostly in the greenhouses. We also have
had them in the controlled temperature rooms at 25°C when seed was being
stored for conditioning in the room. They often appear in the fall in
the greenhouses. They dig up and eat newly planted sprouting seeds, eat
ripe and ripening seeds on the plants, and chew off the heads of wheat.
All seed should be stored in mouseproof containers. Mice are best
eliminated by trapping. Flats with germinating seeds may be protected by
supporting them on glazed crocks. Such flats must be well away from
walls and other objects up which the mice can climb and from which they
can jump onto the flat. Metal screening may also be used to cover the
- 33 -
MANAGEMENT OF FACILITIES
The Phytotron Committee sets the policies for the operation of the
Phytotron. The chairman of the Phytotron Committee is employed full-time
as a scientist but manages the Phytotron and allocates facilities. The
maintenance supervisor is responsible for all maintenance and keeps all
maintenance records. The programmer is responsible for programming all
facilities and for modifying programs/ for minor maintenance, and for
replacing and ordering lamps. The greenhouse supervisor is responsible
for the watering of all plants, preparing pots and soil for seeding, for
discarding soil and plants from completed experiments, and for keeping
the Phytotron facilities and the Phytotron area clean and free of mites,
insects, mice, and diseases.
Each scientist is responsible for completing a Phytotron Program form
(see Appendix No. 5) with the following information: the facility
reguired, the project number and short title, the crop grown, the
scientist's name and office and home phone numbers, the technician's or
associate's name and office and home phone numbers, the date the facility
is required, the estimated time for completion of the experiment, the
date the facility wa • requested, the scientist's signature, lighting,
temperature, humidity, and watering instructions, and any special
Any changes to the program must be in writing on the Shut Down and
Program Change Request form (Appendix 7). The scientist's and
technician's names and phone numbers are required so that they can be
phoned if there is a problem with the growth facility and instructions
are needed concerning the experiment.
Scientists are expected to check lights, temperature, and humidity of the
Phytotron unit they are using throughout the experiment to make sure that
the conditions are exactly what they requested. The scientist is
responsible for seeding all pots and for making all observations and
records of the experiment.
Each scientist is responsible for filling out a Phytotron Work Order form
(see Appendix 6) indicating the number, size, and type of pots required,
the soil mixture or media needed, the type of watering (tap water,
distilled water or a specific nutrient solution), and the greenhouse or
plant growth unit in which the pots or flats are to be placed.
When the experiment has been completed, the scientist fills in the Shut
Down and Program Change Request form (Appendix 7) and informs the
greenhouse supervisor of how the material should be disposed. Plants
infested with insects, infected with disease, or treated with pesticides
are placed in plastic bags and disposed of in a sanitary landfill, while
healthy plants and untreated soil are placed in a compost pile.
All our facilities have routine maintenance at least twice a year (see
Preventative Maintenance form, Appendix 8). After each experiment the
unit is thoroughly cleaned and washed prior to the maintenance
inspection. Three times each week all lights in the phytotron are
inspected and burnt-out bulbs or ballasts are replaced. A record is kept
by the maintenance supervisor of all repairs to each plant growth unit.
- 34 -
GUIDELINES FOR REPORTING PHYTOTRON EXPERIMENTS
Plant growth facilities differ in design, maintenance, air flow patterns,
and other factors which may affect experimental results. Complete and
accurate interpretation of experimental results is difficult or almost
impossible if the environment in the plant growth facility is not
adequately reported. Guidelines for measuring and reporting environmental
factors in controlled environment facilities have been published by Spomer
(1980, 1981) and Sager (1982). Our experience suggests the following
The guidelines are divided into two categories, those which ought to be
reported (essential) and those which ideally should be reported
(desirable). It must be recognized that the measuring equipment and
available staff will influence which of the additional conditions will be
measured. However, the preceding discussion of environmental conditions
should be used as a guide to which of the ideally measured conditions are
likely to be important. Every effort should be made to measure these,
and all that deviate greatly from naive expectations ought to be
reported. These measurements become more important as growing conditions
deviate from 20 to 25°C, as light intensity becomes high, and as daily
air temperatures are varied by more than a few degrees C.
Make and model number of the cabinet or room.
1. Air temperature with a shielded sensor. Specify whether constant
or variable. If variable, give day and night temperatures and
specify nominal rate of change from day to night conditions.
2. If substrate temperature was controlled separately (as in soil
temperature tanks or with heaters or refrigeration coils), provide
set or nominal values and a summary of measured values. Note that if
it was important enough to provide separate temperature control for
substrate temperature, then values ought to be measured and reported
for light and dark periods of the daily cycle.
1. Substrate temperature, if not controlled independently. Measure
at plant crown level for species with crowns below the soil surface
or at least at one shallow depth for other species. Summarize
briefly the results if conditions (air temperature or light) were
cycled. Check and report in summary form if crop was grown long
enough to cause shading of the medium by plant canopy.
2. Leaf temperature. Measure during both the light and dark cycles
for leaves exposed directly to the light and if relevant for those
shaded by upper levels of the plant canopy.
- 35 -
3. Specify types of temperature sensors employed.
4. Tolerance limits during normal cycling of equipment.
1. Specify photoperiod and whether change from dark to light period
was abrupt or gradual. If gradual, indicate how rapidly. State if
photoperiod and thermoperiod coincide and if not, describe difference,
2. Types of lamps used. Provide information on type (e.g.,
incandescent, fluorescent, etc.), power rating and voltage applied,
and phosphor for fluorescent lights.
3. Light intensity. Measure just above the plant canopy or at
medium level at seeding time. Any of the three units described above
may be used but make and model of meter employed should be stated.
When two light sources were used (e.g., incandescent and cool white
fluorescent) give data separately for each light source.
1. Tolerance limits for light intensity. State limits over area of
plant growth at a specified level. State frequency of monitoring of
light intensity and deviation from nominal values permitted.
2. Graph of spectral energy distribution at start of experiment.
State if this was monitored subsequently and what changes occurred.
1. Provide day and night values. Describe type of sensor and
1. Provide tolerance levels.
2. Outline any variations associated with daily cycling of the
cabinet (including those associated with watering) with development
of the crop or in the crop canopy.
1. State how CO2 levels were controlled.
- 36 -
1. Provide data on daily cycling of CO2 levels for a designated
location in or near the plant canopy. Specify measuring device used.
1. Indicate if air flow was up, down or horizontal. Specify how and
where this was measured and provide data.
Containers, media, and nutrients
Note: Literature references should be used where appropriate. In the
absence of such references, all details outlined below should be
1. Containers. State type of container (wood, plastic, glass,
clay), color, and inside dimensions. If a hydroponic system was
used, provide details of construction including information on
monitoring tests used to ensure proper operation.
2. Substrate. Include information on amendments and added
3. State how water and nutrients were supplied (e.g., hose, watering
can, manual hydroponic system, automated hydroponic system, etc.).
4. Nutrient solutions. If a literature reference cannot be
supplied, then a complete list of ingredients including
concentrations must be provided. Frequency of changes of nutrient
solution, frequency and composition of additions to the nutrient
solution, and monitoring techniques should be stated where applicable.
1. If nutrient or water was added manually from a hose or watering
can, temperature and frequency of added water or nutrient should be
specified. Indicate quantities applied. State if water or nutrient
was added directly to the surface of the medium or sprinkled on the
plant canopy. Monitor substrate and canopy temperature changes
associated with watering and describe these.
- 37 -
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Went, F. W. 1957. The experimental control of plant growth. Chronica
Botanica, Waltham, Mass. 343 pp.
Zelitch, I. 1971. Photosynthesis, photorespiration and plant
productivity. Academic Press, New York and London. 347 pp.
- 41 -
Summary of responsibilities
General responsibility for Phytotron
Completing phytotron request form
Filling pots and watering
Special soil or seed treatments
Discarding pots and plants
Repair and maintenance
General surveillance of experiment
Chairman, Phytotron Committee
Scientist or technician
Chairman/ Phytotron Committee
Scientist or technician
Scientist or technician
Scientist or technician
High Ceiling Rooms
Soil Tank Rooms
- 42 -
Plant growth rooms
5.05 x 3.35
5.05 x 3.35
5.05 x 3.07
5.05 x 3.35
5.11 x 3.81
5.11 x 3.81
5.11 x 3.81
5.11 x 3.81
TOTAL GROWTH ROOM AREA
Plant growth room benches
Propagation Room Benches
Room No. No. Benches
Bench area (m 2 )
High Ceiling Room Benches
1.30 x 5.05
1.30 x 5.05
1.30 x 5.05
1.30 x 5.05
Soil Tank Room Benches
1.45 x 5.05
1.45 x 5 05
1.45 x 5.05
1.45 x 5.05
TOTAL PLANT GROWTH AREA
Experimental rooms with limited light
Room No. Temp. (°C)
SC-17C -20 to +25
SC-23A -20 to +25
Area (m 2 )
- 45 -
PHYTOTRON PROGRAM FORM
COMPLETE SECTIONS: 1-2-3
fXl ALL APPROPRIATE BOXES
CABINET REQUIRED # _
TITLE OF EXPERIMENT
SECTION "2" IN THE EVENT OF CABINET MALFUNCTION - AFTER 4:30 PM AND WEEKENDS
\ZD 1) NOTIFY SCIENTIST CH IF NO ONE CAN BE REACHED: EZI - SHUTDOWN UNTIL SCIENTIST
NOTIFY ALTERNATE LJ CAN BE REACHED
I I - CALL MAINTENANCE STAFF
| I - SHUTDOWN TILL NEXT
I 1 2) SHUTDOWN AND CALL MAINTENANCE STAFF IMMEDIATELY
I I 3) SHUTDOWN UNTIL NEXT WORKING DAY
SECTION "4" FOR PROGRAMMER USE ONLY
SECTION "5" - PROGRAM INSTRUCTIONS
1) LIGHTING: FLUORESCENT COOL WHITE EZ1 INCANDESCENT BULBS EZ1
FLUORESCENT GROW LUX WS I i NO INCANDESCENT BULBS LZZI
2) LIGHTS ON AM | | PM | [
LIGHT INTENSITY 1/3 I I 2/3 | | FULL | I
LIGHTS ON AM I | PM | |
'NOTE - ANY FURTHER LIGHTING INSTRUCTIONS LIST ON REVERSE SIDE.
3) TEMPERATURE: DAY
'NOTE - ANY FURTHER TEMPERATURE INSTRUCTIONS LIST ON REVERSE SIDE.
4) RELATIVE HUMIDITY: DAY 1
***NOTE - ANY FURTHER INSTRUCTIONS LIST ON REVERSE SIDE.
5) DATE EXPERIMENT WILL ENTER CABINET
♦""ATTENTION: NO PROGRAMMING ONE DAY BEFORE A HOLIDAY
MINIMUM OF FIVE WORKING DAYS NOTICE FOR START-UPS, IN ADVANCE
- 46 -
AGRICULTURE CANADA RESEARCH STATION
Lethbridge, Alberta TlJ 4B1
PHYTOTRON WORK ORDER
Work Order No.
Section: AS CE PP PS SS VM ADA
Location: Greenhouse No.
work required: ALLOW 7 WORKING DAYS FOR COMPLETION OF ORDER
Containers filled: Type and Size
Soil Mixture (ratio) : Soil
Containers emptied: No.
Pest Control: Type
To Compost Pile
(Greenhouse Use Only)
Date started Date Completed
Work Order No.
Date order received
Expected completion date as requested
- 47 -
SHUT-DOHN AND PROGRAM CHANGE REQUEST
COMPLETE ONLY THOSE SECTIONS WHICH PERTAIN TO YOUR NEEDS: [X] ALL APPROPRIATE BOXES
DATE ACTION REQUIRED
I WILL NOT BE REUSING THIS CABINET ... □
I WILL BE USING THIS CABINET AGAIN ... □ DATE OF RE-USE
CHANGE: LIGHT INTENSITY - OFF
DATE ACTION REQUIRED
CHANGE: TEMPERATURE - NEW TEMPERATURE; DATE ACTION REQUIRED
CHANGE: RELATIVE HUMIDITY - NEW SETTING; DATE ACTION REQUIRED
*****ATTENTION - FOR ANY CHANGE IN DAYLIGHT DURATION OR THE START OF A NEW EXPERIMENT A
NEW PROGRAM MUST BE SUBMITTED.
- 48 -
t ***FOR GREENHOUSE AND MAINTENANCE USE ONLY'
THIS CABINET WILL BE READY FOR RE-USE ON (DATE)
THIS CABINET WAS CLEANED AND READY FOR RE-USE (DATE) _
THIS CABINET IS ON TEST DATE:
IN THE EVENT OF A MALFUNCTION 1) call Carey Jackson (Maintenance - 395 or page)
2) after hours - call C. Jackson @ 345-2393
- if no answer, shut cabinet down and
indicate on commissionaire's report
New temp, required:
High limit set I |
Low limit set I j
Computer center notified . . | |
Audible alarm on | |
Circuit breakers/fuses .... | |
Circulation fans | |
Aspirator fan | |
Light switches set | ]
Heater switches set | |
Temperature/humidity recorder | |
Temperature program timer set | |
Humidity program timer set | |
Defrost limit set (max +7°C) I I
Dampers on correct coil | I
Top defrost heater limit set (max. +10°C) I I
Bottom defrost heater limit set (max. +10°C) ... | I
Pilot lights operating | |
- 49 -
Long-term averages and extremes of air temperature (°C), 1902-1985,
Frost data, 1902-1985, Lethbridge
Last frost in spring (0°C)
First frost in fall (0°C)
No. of frost-free days
Apr 26 1940
Aug 14 1928
Jul 3 1979
Oct 14 1928
Last killing frost in spring (-2°C) May 7 Jun 2 1984
First killing frost in fall (-2°C) Sep 25 Sep 3 1962 Oct 22 1984
No. of crop days 140 110 (1921) 178 (1940)
- 50 -
1 1 1 1 —
JAN FEB MAR APR MAY
JUL AUG SEP OCT NOV DEC
Mean soil temperature at three depths, 1967-1985,
Average monthly growing degree-days, heating
degree-days, and corn heat units in the Lethbridge area
- 51 -
Long-term averages and extremes of precipitation and snowfall, 1902-1985,
Percent probability of growing season rainfall, Lethbridge
Lethbridge sunshine data, 1909-1985
-L C J- \_ t; 11 I*
- 53 -
To Convert From*
Ounce (U. S. Fluid)
Quart (U. S. Liq. )
Ton of regrigeration
(U. S. Comm.)
Ton of refrigeration
Ton (short) = 2000 lb
m 3 min~l
cal cm~ 2 min - ^
kg m -2
kg m~ 3
Btu hr" 1
kg cal hr - -'-
cal cm -2 min - -*-
erg sec - -*- cm -2
1 x 10'
*To facilitate conversion, the time units are those customarily used
in the past with the f. p. s. system; i.e., feet per min. x .3048
would convert to meters per minute in preference to m/sec.
(From Downs and Bonaminio 1976)
- 54 -
Make up in bushel tubs (35.2 liter)
Add in proportion by volume
2 parts peat moss
2 parts No. 3 grade (medium) vermiculite
1 part sand
To each tub add:
165 g CaC0 3
38 g 0-45-0 fertilizer
150 g Osmocote 18-6-12
1 g 300 FE sequestrene
2 g fritted trace elements
(Adapted from Boodley and Sheldrake 1977)
Hoagland's no. 1 nutrient solution
All chemicals dissolved in distilled water.
Nutrient is made up in 20 liter plastic carboys.
Approximately 10 liters of distilled water
17 ml 1 M KH 2 P0 3
17 ml Micronutrient solution*
33 ml 1 M MgS0 4
81 ml 1 M KN0 3
81 ml 1 M Ca(N0 3 ) 2
1.35 g Iron citrate dissolved by heating in approximately 1 liter
Distilled water to make up to 20 liters
1 liter contains
2.86 g boric acid (H3BO3)
1.81 g manganese chloride (MnCl2 • 4H 2 0)
0.22 g zinc sulphate (ZnS0 4 • 7H 2 0)
0.08 g copper sulphate (CuS0 4 • 5H 2 0)
0.02 g molybdic acid (H 2 Mo0 4 • H 2 0)
(Adapted from Hoagland and Arnon 1950)
- 55 -
CONVERSION OF UNITS
Conversion of Photon Units to Radiometric Units
Conversion of quantum sensor output in ^E s' 1 nr 2 (400-700 nm) to
radiometric units in W nr 2 (400-700 nm) is complicated. The conversion
factor will be different for each light source, and the spectral distribution
curve of the radiant output of the source (W\ ; W nr 2 nm 1 ) must be known
in order to make the conversion. The accurate measurement of W\ is a
difficult task, which should not be attempted without adequate equipment
and calibration facilities. The radiometric quantity desired is the integral of
Vv\ over the 400-700 nm range, or:
W x d\
At a given wavelength X, the number of photons per second is
photons s =
where h = 6.63 • 10 -34 joule-s (Planck's constant), c = 3.00 • 10 8 m s -1
(velocity of light) and X is in nm. hc/X is the energy of one photon. Then,
the total number of photons per second in the 400-700 nm range is
This is the integral which is measured by the sensor. If ft is the reading of
the quantum sensor in ^E s 1 nr 2 (1 /iE s -1 nr 2 ■ 6.022 • 10 17 photons s" 1
m" 2 ), then
•oo L,_/ v
Combining Eq. (1) and Eq. (4) gives
W T = 6.022 • 10 17 (Rhc)
10 17 (Rhc) J -?
W x dx
XW X dX
To achieve the two integrals, discrete summations are necessary. Also,
since W x appears in both the numerator and the denominator, the nor-
malized curve N x may be substituted for it. Then
2 N X ^X
W T = 6.022- 10 17 (Rhc)
2 X ^£ X
where AX is any desired wavelength interval, Xj is the center wavelength
of the interval and Nxj is the normalized radiant output of the source at the
center wavelength. In final form this becomes
W T = 119.8 (R)
2 N M
where R is the reading in /xE s -1 nr 2 .
The following procedure should be used in conjunction with Eq. (7).
1. Divide the 400-700 nm range in i' intervals of equal wavelength spac-
2. Determine the center wavelength (Xj) of each interval.
3. Determine the normalized radiant output of the source (Nx,) at each of
the center wavelengths.
4. Sum the normalized radiant outputs as determined in Step 3 to find
5. Multiply the center wavelength by the normalized radiant output at that
wavelength for each interval.
6. Sum the products determined in Step 5 to find IXjNx:.
7. Use Eq. (7) to find Wj in W nr 2 , where R is the quantum sensor out-
put in fit s' 1 nr 2 .
The following approximation assumes a flat spectral distribution curve of
the source over the 400-700 nm range (equal spectral irradiance over the
400-700 nm range) and is shown as an example.
Given: i = 1
AX = 300 nm
.Xj = 550 nm
WT - «" (R> ( Z^f^ ) = 2%P = 022(H) W m- 2
1 550 • N (550) 550
1 w nr 2 - 4.6 mE s -1 nr 2
This conversion factor is within ±8.5% of the factors determined by
McCree as listed in Table I (8).
Conversion of Photon Units to Photometric Units
To convert photon units (/xE s" 1 nr 2 , 400-700 nm) to photometric units
(lux 400-700 nm), use the above procedure, except
a) Replace Eq. (1) with
Lux = 683 J«. yxw x dx
where yx is the luminosity coefficient of the standard CIE curve with
yx = 1 at 550 nm and Wx is the spectral irradiance (W nr 2 nm 1 ).
b) Replace Eq. (5) with
Lux = (683)
J yx Wx dx
(6.022 • 10 17 ) (Rhc) J ~/ X
L xw ^
c) Replace Eq. (6) with
2 v Xj N Xi AX
Lux = (683) (6.022 • 10 17 ) (Rhc)
2 x i N X| AX
d) Replace Eq. (7) with
2 v Xj Nxj
Lux = 8.17- 10*(R)-!-
2 xN Xi
e) Replace Step 4 with:
4a) Multiply the luminosity coefficient (yx) of the center wavelength by
the normalized radiant output (N K ) at that wavelength for each
4b) Sum the products determined in Step 4a to find I yx; Nx:.
i ' '
The following approximation assumes a flat spectral distribution curve of
the source over the 400-700 nm range (equal spectral irradiance over the
400-700 nm range) and is shown as an example.
Given: i = 1 to 31
AX = 10 nm
X,= 400, X 2 = 410, X 3 = 420 X 31 = 700
Nx = 1 for all wavelengths
yx, = 0.0004, yx 2 = 0.0012, yX 3 = 0.004 yx 3 , = 0.0041
2 y Xj
Lux = 8.17- 10«(R)-!. = 8.17.10 4 (R)(-^T-)
2 x i
Lux = 51.2 R, where R is in ^E s 1 nr 2
1000 lux = '1 klux = 19.5 mE s" 1 nr 2
(From LI-COR 1979)
- 56 -
Top left. The main floor phytotron at the
Lethbridge Research Station.
Top right. Examining plant in a
Middle left. Barley growing in cylinders
Middle right. Mature wheat in a
Bottom left. Corn in a high-ceiling
Bottom right. Pollinating wheat in a
BIBLIOTHEQUE CANADIENNE DE I'AGRICULTURE
3 TD73 0011fl072 D